Cover crops can be an effective means to protect soil and reduce risks of erosion in olive groves. However, for this protection to be significant, the vegetation must attain a significant amount of ground cover, which is estimated to be at least 30% during the rainy season. In olive groves on degraded soils, which occupy large surface areas in the olive-growing areas of the Mediterranean region, the establishment of cover crops may be an arduous challenge, particularly in areas with a high density of rabbits. In this study, we have selected two olive orchards with scarce natural vegetation located in Andalusia (southern Spain), in which rabbit populations intensively forage the cover crops, to test whether the self-seeding of an unpalatable species corn chamomile (Anthemis arvensis L.; A. arvensis for short) could achieve sufficient coverage for soil protection, in the year following that in which the broadcast-seeding was carried out for the implementation of cover crops. The hand broadcast-seeding of A. arvensis was carried out on sixteen elementary plots in the lanes of the two olive orchards in the autumn of 2015, and seed germination in the subsequent self-seeding took place in the autumn of 2016. The plant height and A. arvensis ground cover in these plots were measured throughout the two growth cycles, and aerial biomass was measured at maturity. The results showed that there were no significant differences in the maximum plant height between the two growth cycles (mean ± SD of 21.2 ± 1.6 cm), while the ground cover was significantly greater in the case of self-seeding, especially during the winter (37.2 ± 8.1 and 9.3 ± 6.7% for self-seeding and broadcast-seeding, respectively), and aerial biomass at maturity had more than doubled (99.7 and 43.9 g m⁻², respectively). These data suggest that this unpalatable species could establish an effective herbaceous cover by means of self-seeding in olive groves on degraded soils that are being overgrazed owing to the high pressure of rabbits. Despite the poor establishment in the broadcast-seeding year, our findings indicate that A. arvensis might be an alternative cover crop that could help the sustainability of these threatened olive groves. Its high seed production (2000 to 4000 seeds per plant), and an early emergence just after the first autumn rains, should result in an increased ground cover by A. arvensis during the rainy season in the subsequent years of self-seeding. This, therefore, could contribute to soil conservation, in addition to providing other benefits of increased biodiversity and improvement for agricultural landscapes.

中文翻译：

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强烈放牧条件下橄榄林中抗南芥的自种花粉

覆盖作物可以成为保护土壤并减少橄榄树林遭受侵蚀的有效方法。但是，要使保护效果显着，植被必须获得大量的地被，估计在雨季至少有30％。在退化土壤的橄榄树中，这些橄榄树在地中海地区的橄榄种植区占据很大的表面积，建立覆盖作物可能是一项艰巨的挑战，特别是在兔子密度高的地区。在这项研究中，我们选择了安达卢西亚（西班牙南部）的两个天然植物稀少的橄榄果园，其中兔子种群对草料作物进行集约化饲喂，以测试是否有不宜食用的玉米洋甘菊（Anthemis arvensis L. ; A. arvensis在接下来的一年中，为了实施覆盖作物而进行了播种。2015年秋季，在两个橄榄果园的车道上的十六个基本地块上进行了人工播种播种的A. arvensis，随后的自种过程中的种子发芽在2016年秋天进行。株高和Arvensis这些地块的地表覆盖度是在两个生长周期内测量的，而空中生物量是在成熟时测量的。结果表明，两个生长周期之间的最大植株高度没有显着差异（平均±SD为21.2±1.6 cm），而在自种的情况下，尤其是在冬季，地面覆盖明显更大（自种和播种分别为37.2±8.1和9.3±6.7％，成熟时的空中生物量增加了一倍以上（99.7和43.9 gm ^-2）， 分别）。这些数据表明，这种难吃的物种可以通过在由于兔子高压而过度放牧的退化土壤上的橄榄树中自种，从而建立有效的草本覆盖。尽管播种年度的收成不好，但我们的研究结果表明，A。arvensis可能是一种替代性的有盖作物，可以帮助这些受威胁的橄榄树的可持续性。它的高种子产量（每株植物2000到4000粒种子），以及在第一次秋季降雨之后的早期出现，应导致A. arvensis的地面覆盖增加在接下来的几年中的自我播种的雨季。因此，除了提供增加生物多样性和改善农业景观的其他好处外，这还可以促进土壤保护。